Molecular regulation of PPARγ/RXRα signaling by the novel cofactor ZFP407

Ockunzzi, J.; Buchner, D. A.; Charrier, A.; Ghanta, S. V.

Cofactors interacting with PPAR{gamma} can regulate adipogenesis and adipocyte metabolism by modulating the transcriptional activity and selectivity of PPAR{gamma} signaling. ZFP407 was previously demonstrated to regulate PPAR{gamma} target genes such as GLUT4, and its overexpression improved glucose homeostasis in mice. Here, using a series of molecular assays, including protein-interaction studies, mutagenesis, and ChIP-seq, ZFP407 was found to interact with the PPAR{gamma}/RXR protein complex in the nucleus of adipocytes. Consistent with this observation, ZFP407 DNA binding sites significantly overlapped with PPAR{gamma} sites, with more than half of ZFP407 binding sites overlapping with PPAR{gamma} DNA binding sites. Transcription factor binding motifs enriched in these overlapping sites included GFY-Staf, ELF1, ETS, ELK1, and ELK4, which regulate key functions within adipocytes. Site-directed mutagenesis of frequent PPAR{gamma} phosphorylation or SUMOylation sites did not prevent its regulation by ZFP407, while mutagenesis of ZFP407 regions necessary for RXR and PPAR{gamma} binding abrogated any impact of ZFP407 on PPAR{gamma} activity. These data suggest that ZFP407 controls the activity of PPAR{gamma}, but does so independently of post-translational modifications, likely by direct binding, establishing ZFP407 as a newly identified PPAR{gamma} cofactor. In addition, ZFP407 was also found to bind to DNA in regions that did not overlap with PPAR{gamma}. These DNA binding sites were more significantly enriched for the transcription factor binding motifs of GFY and ZNF143, which may contribute to the non-PPAR{gamma} dependent functions of ZFP407 in adipocytes and other cell types.